For several decades, testosterone preparations have been used clinically to treat primary and secondary male hypogonadism in order to achieve normal physiologic levels of testosterone and to relieve symptoms of androgen deficiency. Furthermore, testosterone preparations have been used in male contraception as the sole active therapeutic agent for suppressing spermatogenesis or as an active agent in combination with progestins or further gonadotropin suppressive agents.
Male hypogonadism is characterised by a deficiency of endogenous testosterone production resulting in abnormally low levels of circulating testosterone, i.e. serum testosterone levels below 10 nmol/l.
Male hypogonadism may be classified in primary and secondary causes: primary or hypergonadotropic hypogonadism, congenital or acquired, may be derived from testicular failure due to cryptorchidism, bilateral testicular torsion, orchitis, orchidectomy, Klinefelter syndrome, chemotherapy or toxic damage from alcohol or heavy metals.
Secondary or hypogonadotropic hypogonadism, congenital or acquired, is caused by idiopathic gonadotropin releasing hormone (GnRH) deficiency or pituitary-hypothalamic injury from tumours, trauma, or radiation. In the vast majority of cases, hypogonadism is related to a primary defect of the testes.
The clinical picture of hypogonadal adult men varies a lot. For example, testosterone deficiency is accompanied by symptoms of different severity, including sexual dysfunction, reduced muscle mass and muscle strength, depressed mood and osteoporosis.
Current standard therapies aims at restoring physiologically relevant levels of testosterone in serum, which applies to concentrations of about 12 nmol to about 36 nmol. Intramuscular injection of testosterone esters, such as testosterone enanthate or testosterone cypionate, administered every two to three weeks, still represents the standard of testosterone replacement therapy in most countries of the world. Apart from the inconvenience of frequent visits to the doctor's office, the patients complain about variations in well-being due to short-term fluctuations of serum testosterone levels resulting from the pharmacokinetic profile after intramuscular injection of for example testosterone enanthate.
Recently, the use of testosterone esters with longer aliphatic chain length and/or higher hydrophobicity, such as testosterone undecanoate, has become interesting in terms of prolonging the interval between injections. Longer intervals between injections are advantageous from a patient's point of view.
For example Zhang G et al, 1998, report the injection of compositions comprising testosterone undecanoate in a concentration of 250 mg in 2 ml tea seed oil so as to administer a dose of 500 mg or 1000 mg of testosterone undecanoate (Zhang G et al., A pharmacokinetic study of injectable testosterone undecanoate in hypogonadal men. J Andrology, vol 19, No 6, 1998). Zhang et al, 1999, relates to injectable testosterone undecanoate as a potential male contraceptive (Zhang et al, J clin Endocrin & metabolism, 1999, vol 84, no 10, p 3642-3646).
Furthermore, Behre et al, 1999, relates to testosterone undecanoate preparations for testosterone replacement therapy such as testosterone undecanoate 125 mg/ml in teaseed oil and testosterone undecanoate 250 mg/ml in castor oil (Behre et al, Intramuscular injection of testosterone undecanoate for the treatment of male hypogonadism: phase I studies. European J endocrin, 1999, 140, p 414-419).
Intramuscular injections of 250 mg testosterone undecanoate and 200 mg MPA every month have been suggested for male contraception (Chen Zhao-dian et al, clinical study of testosterone undecanoate compound on male contraception. J Clin androl, 1986, vol 1, issue 1, abstract)
Wang Lie-zhen et al. report testosterone replacement therapy using monthly intramuscular injections of 250 mg testosterone undecanoate (Wang Lie-zhen et al. The therapeutic effect of domestically produced testosterone undecanoate in Klinefelt syndrome. New Drugs Market 8: 28-32, 1991.
WO 95/12383 (Chinese application) relates to injectable compositions of testosterone undecanoate in vegetable oils, optionally in admixture with benzyl benzoate. The compositions are injected monthly when applied for male contraception and substitution therapy.
U.S. Pat. No. 4,212,863 is a patent which relates to a lipid formulation of steroids for oral or parenteral administration various oil carriers, optionally including benzyl benzoate, which is said to lower the viscosity of the lipid carrier and/or enhance the solubility.
Eckardstein and Niesclag, 2002, report the treatment of hypogonadal men with testosterone undecanoate, wherein physiological relevant levels of testosterone may be achieved for an extended period of time upon initially injecting testosterone undecanoate four times in intervals of 6-weeks followed by subsequent injections of longer intervals (Eckardstein and Niesclag, treatment of male hypogonadism with testosterone undecanoate injected at extended intervals of 12 weeks, J Andrology, vol 23, no 3, 2002)
However, it is well known that therapies with testosterone esters, such as testosterone undecanoate, still need to be improved in terms of achieving reliable serum testosterone levels in the physiologically acceptable range for a prolonged period of time. There is a need of providing reliable standard regimens acceptable for a broad population of men in need thereof, preferably regimens without the need of occasional control of serum testosterone levels, and regimens wherein steady state conditions are achieved within a shorter time period.